1. Field of the Invention
The invention relates to a portable radio unit for use in a mobile telephone system and, more particularly, a portable radio unit having a battery saving function and a control method thereof.
2. Description of Related Art
A technique in the field of mobile telephone system is disclosed, for example, in Japanese Patent Kokai No. 9-275587.
In a mobile telephone system, a service range is defined by a plurality of base stations and portable radio units perform communication operations when located in such a communicatable service range. For enabling the operation of a portable radio unit, it is necessary to maintain the unit in a usable state for a long-time by electric power stored in a battery which has a limited capacity.
The reduction of power current consumption of a portable radio unit, therefore, is one of important elements to decide the performance of the portable radio unit. Although a circuit design to reduce the current consumption has obviously been made hitherto, further, a method whereby even in a wait standby mode, a low electric power consumption mode is set or a power supply is stopped with respect to circuits except for the circuit which is actually operating is used.
The method of stopping the power supply to the circuits other than the actually operating circuit at the time of use will now be described with respect to a digital mobile telephone system as an example.
A portable radio unit of the digital mobile telephone system receives all of the frequencies peculiar to providers after a power source has been turned on and checks whether there is a channel whose reception level exceeds a threshold level. The threshold level is previously determined based on a reception level necessary to surely capture control information in the channel that is transmitted from the base station, continually.
If there is a relevant channel, whether the portable radio unit is located in the service range of the base station or not is discriminated, while the synchronization with that channel is established, depending on whether the control information in the channel can be received or not. When the control information can be received, it is determined that the portable radio unit is located in the service range of the base station. In this instance, the portable radio unit transmits its position information to the base station (position registration) and stores the received control information (identification information or the like of the base station).
The portable radio unit, therefore, is connected to a radio line through the base station and enters a standby mode. Once the portable radio unit enters the standby mode, it intermittently receives only the slot at the timing when the self portable radio unit is designated among the signals which are transmitted at a predetermined period from the base station, thereby enabling a call to be received. A method, therefore, whereby the shift to the low electric consumption state or the stop of the power supply is performed in a mode other than the reception mode to the circuit whose operation is unnecessary, thereby reducing the current consumption, has been used hitherto.
When the channel which exceeds the threshold level cannot be captured or, even if it can be captured, when the control information in the channel cannot be received, it is determined that the portable radio unit is located out of the service range. After that, until the portable radio unit moves into the service range of the base station and can receive the control information, a series of operations (control information capturing operation) is repeated until whether the portable radio unit is located in the service range or out of the service range is discriminated.
That is, in the portable radio unit, the control information capturing operation is repeated when the user is out of the service range of the radio base station or when the user is out of the service range because he is at a place where the radio wave does not reach (for example, in an underground area, in a building having a reinforced structure, or the like) although the area lies within the service range. Therefore, a receiving circuit and the other peripheral circuits always have to be in the operating state. There is, consequently, a problem such that when the user is out of the service range for a long time, although there is not a possibility that the portable radio unit enters the wait standby mode for this period of time, the receiving circuit and the peripheral circuits are made operative in vain, so that an electric power of a battery is consumed.
For example, in the apparatus disclosed in Japanese Patent Kokai No. 9-275587, the user himself can arbitrarily set and change a stop time of the receiving operation of an intermittent receiving process when he is out of the service range. Since the power supply to the receiving means is interrupted or the electric power consumption is reduced by electric power consumption suppressing means during the halt of the receiving operation of the intermittent receiving process, a battery saving effect is obtained.
A method is also disclosed wherein as the number of continuous times of determination that the user is out of the service range is larger, namely, as the time when the user stays out of the service range is longer, the receiving operation halt time of the intermittent receiving process of the control information for the returning to a place within the service range is automatically extended after completion of the discrimination that the user is out of the service range.
According to this method, battery saving which is settled to the receiving operation stop time whose upper limit is set and accords with a use situation of the portable radio unit of each user can be realized.
It is, however, difficult for the general user of the portable radio unit to understand a meaning of xe2x80x9csetting of the intermittent receiving time when the user is out of the service rangexe2x80x9d. Most of the users, further, do not read the operating instructions of the using method. There is, consequently, a problem that even if xe2x80x9cthe setting functionxe2x80x9d as shown in the conventional technique exists, it is not used in many cases.
There is further a problem that, in many cases, when the receiving interval is extended at xe2x80x9cthe number of continuous times of determination such that the user is out of the service rangexe2x80x9d, the optimum control is not performed in the actual use environment.
The invention has been made in consideration of the drawbacks mentioned above and it is an object of the invention to provide a control method of a portable radio unit for use in a mobile telephone system which can realize battery saving according to a use situation without allowing the user to set parameters when he is out of a service range.
To accomplish the above object, according to a first aspect of the invention, there is provided a control method of a portable radio unit for use in a system comprising the steps of: (a) measuring a reception intensity of control information by a reception intensity detector; (b) time-sequentially linear-predictive analyzing the measured reception intensity by a linear prediction analyzer; (c) predicting a reception intensity at a next time; (d) setting a receiving interval of the control information on the basis of the predicted reception intensity; (e) measuring the reception intensity of the control information on the basis of the set receiving interval; (f) decimating the measured reception intensity on the basis of a receiving interval set by an intermittent receiving interval updater; and (g) saving an electric power consumption of a battery in a wait standby mode by repeating the series of operations (a) to (f).
According to a second aspect of the present invention, in the portable radio unit according to the first aspect, a fluctuation period of the reception intensity is obtained by using a prediction coefficient calculated to predict the reception intensity at the next time, and it is controlled so as to extend the receiving interval in the case where the obtained fluctuation period becomes so short as to obstruct a talking and the reception intensity is also small.
According to a third aspect of the present invention, in the control method of a portable radio unit according to the first or second aspect, a hardware scale is reduced by using the linear prediction analyzer in common with an audio encoder.
According to a fourth aspect of the invention, in the control method of a portable radio unit according to the first, second or third aspect, the intermittent receiving interval is controlled in accordance with a battery residual amount by adding a battery residual amount detecting function.
According to a fifth aspect of the present invention, in the control method of a portable radio unit according to the fourth aspect, by adding a battery charging interval learning function, the intermittent receiving interval is controlled in accordance with a prediction value of a time that is required until a portable radio unit is set to a charger and the battery residual amount.
According to a sixth aspect of the present invention, in the control method of a portable radio unit according to the fifth aspect, by adding a talking time learning function, the intermittent receiving interval is controlled in accordance with the prediction value of a time that is required until the portable radio unit is set to the charger, an average talking time, and the battery residual amount.
According to a seventh aspect of the present invention, there is also provided a portable radio unit for use in a mobile telephone system having a function to measure an elapsed time after completion of a transmitting or receiving operation, wherein an intermittent receiving interval of a control signal is controlled in accordance with the elapsed time after completion of the operation, and an electric power consumption of a battery in a wait standby mode is saved.
According to a eighth aspect of the present invention, in the control method of a portable radio unit according to the first, second, third, fourth, fifth, or sixth aspect, a function to measure an elapsed time after completion of a transmitting or receiving operation is added, a multiplier according to the elapsed time after completion of the operation is replaced to a linear filter whose high band is attenuated, and the intermittent receiving interval is controlled in accordance with a reception field intensity.